Tn7 is an E. coli transposable element which encodes resistance to trimethoprim, streptomycin and spectimomycin. In contrast to most other transposable elements, which transpose at low frequency with little specificity, Tn7 can transpose with high efficiency to a specific chromosomal site called attTn7. When attTn7 is unavailable, Tn7 transposes with reduced frequency and specificity. Tn7 is a complex transposon: the cis-acting DNA sites at attTn7 and at the ends of Tn7 which participate directly in transposition are large and elaborate, Tn7 encodes 5 proteins required for transposition and host-encoded proteins are also known to be required. The long-range goals of this project are to understand at the molecular level the mechanism of Tn7 transposition and how the expression of the genes encoding the proteins which govern transposition is regulated. The approaches here to define the mechanism of transposition are several-fold: (1) to directly examine substrate DNA molecules in vivo during transposition, and (2) to examine in vitro interactions between the trans-acting transposition proteins and the cis-acting sites they recognize. This analysis will be augmented by mutational analysis of the cis-acting sites. This work will also begin to define the regulatory circuitry of the genes encoded by Tn7 which govern transposition. Elucidation of the mechanism of Tn7 transposition will provide information about two basic cellular processes important in both procaryotes and eucaryotes: DNA rearrangements and the control of gene expression. Moreover, understanding Tn7 transposition will also contribute to understanding the rapid dispersal of antibiotic resistance determinants.